1. Field of the Invention
This invention relates to the field of surfactants and more particularly to a surfactant which enables the manufacture of emulsion polymers at high solids levels.
2. Description of the Prior Art
Vinyl acetate copolymer emulsions having a solids content of 65% by weight are known and some are articles of commerce. Such emulsions, however, often require high levels of surfactant or protective colloid to achieve the required stability to shearing forces and to freezing. In addition, such techniques as delayed surfactant addition or the use of monomer pre-emulsions are often required in order to achieve manageable viscosities. These departures from conventional practice, while successfully producing 65% solids latexes, can lead to undesirable properties such as reduced resistance to moisture and unsatisfactory rheological properties. The variations from conventional procedures may also require equipment changes and result in a more expensive process.
High solids vinyl acetate emulsion polymers are prepared by various methods. Such polymers may be prepared using pre-emulsified monomers or using a higher than normal surfactant level. Still another method uses delayed surfactant addition. U.S. Pat. No. 4,409,355 uses a multistage monomer addition to prepare latexes with 60% or more solids. In U.S. Pat. No. 3,423,353, large increments of initiator are added after the reaction is completed to achieve the desired viscosity.
Accordingly, it is an object of the present invention to provide a surfactant which eliminates the need for such complex methods for preparing high solids emulsion polymers. It is a related object of the present invention to provide a surfactant which may be used to prepare stable, high solids emulsion polymers simply and economically.